We continue to study the prevalence and specificity of placental proteins (chorionic gonadotropic and its free alpha (alpha) and beta subunits (CG-beta), placental lactogen, placental alkaline phosphatase, and pregnancy-specific beta1-glycoprotein (SP1) as cancer markers in vivo and in vitro. Study of more than 1000 sera from cancer patients and patients with a variety of non-malignant disorders reveals a higher prevalence of alpha and CG-beta compared to pituitary beta subunits (LH-beta, FSH-beta and TSH-beta). In a study of 42 malignant lines and 18 normal fibroblast strains in vitro, a similar higher prevalence of ectopic alpha and CG-beta relative to pituitary LH-beta, FSH-beta, growth hormone and prolactin was observed. At the levels of detection used, ectopic PL production was not detected. These data suggest that ectopic production of even closely related proteins is not a random process. SP1 has been found in cultures of normal human fibroblasts.